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United States Patent |
5,175,577
|
Shinozaki
,   et al.
|
December 29, 1992
|
Drive member sensing arrangement for an automatic focusing system of a
camera
Abstract
An automatic focusing system for a camera comprises a motor rotatable in
opposite directions, a drive member driven for rotation by the motor, a
distance-setting member rotatable together with the drive member to place
an objective lens in an initial position and movable to a predetermined
forward position, and a holding mechanism for holding the distance-setting
member in the predetermined forward position. The position of the drive
member is identified at each monitoring point, and a position
identification signal is generated. The sequence of movement of the
distance-setting member is analyzed from a starting position to the
predetermined forward position. The system further provides for preventing
improper holding of the distance-setting member at its initial position.
Inventors:
|
Shinozaki; Nobuo (Chiba, JP);
Koizumi; Hiroyuki (Chiba, JP);
Takami; Atsushi (Chiba, JP);
Ishikawa; Tadashi (Chiba, JP)
|
Assignee:
|
Seikosha Co., Ltd. (Tokyo, JP)
|
Appl. No.:
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798352 |
Filed:
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November 21, 1991 |
Foreign Application Priority Data
Current U.S. Class: |
396/90 |
Intern'l Class: |
G03B 013/36 |
Field of Search: |
354/400-409,234.1,435,439,195.1
|
References Cited
U.S. Patent Documents
4348089 | Sep., 1982 | Shenk | 354/195.
|
4881096 | Feb., 1987 | Ogihara et al. | 354/400.
|
4918479 | Apr., 1989 | Inoue et al. | 354/400.
|
Primary Examiner: Perkey; W. B.
Attorney, Agent or Firm: Jordan and Hamburg
Parent Case Text
This application is a continuation, of application Ser. No. 07/543,624,
filed Jun. 26, 1990, now abandoned.
Claims
What we claim is:
1. An automatic focusing system for a camera comprising a motor rotatable
in forward and reverse directions, a drive member driven for rotation in
said directions by said motor, a distance-setting member having an initial
position at which an objective lens is located prior to a focussing
operation, said distance-setting member being rotatable together with said
drive member to predetermined forward positions, a holding mechanism for
holding said distance-setting member at said initial and a predetermined
one of said forward positions, and being moved out of engagement with said
distance-setting member during a focusing operation of said objective lens
by reverse movement of said drive member, detecting means for detecting
the positions of said drive member at a plurality of monitoring points
independently of the position of said distance setting member after said
reverse movement of said distance-setting member, said detecting means
being operable to generate a position identification signal, and control
means for controlling said motor for the sequence of movements of said
drive member from a starting position to said predetermined one of said
forward positions.
2. An automatic focusing system for a camera comprising a motor rotatable
in forward and reverse directions, a drive member driven for rotation in
said directions by said motor, a distance-setting member having an initial
position at which an objective lens is located prior to a focussing
operation, said distance-setting member being rotatable together with said
drive member to predetermined forward positions, a holding mechanism for
holding said distance-setting member at said initial and a predetermined
one of said forward positions, and being moved out of engagement with said
distance-setting member during a focusing operation of said objective lens
by reverse movement of said drive member, detecting means for detecting
the position of said drive member at a plurality of monitoring points
independently of the position of said distance setting member after said
reverse movement of said distance-setting member, said detecting means
being operable to generate a position identification signal, and control
means for controlling said motor for the sequence of movements of said
drive member from a starting position to said one of said predetermined
forward positions, said control means comprising means for selectively
preventing holding of said distance-setting member at said initial
position.
3. An automatic focusing system for a camera having a drive member for
controlling the operation of a shutter, a reversible stepping motor for
moving said drive member in forward and reverse directions, a source of
pulses coupled to said motor, a distance setting member for controlling
the position of a lens, means for coupling said distance setting member to
said drive member for movement therewith from an initial position, means
responsive to reverse direction movement of said motor for moving said
drive member and distance setting members to said initial position, means
responsive to forward direction of movement of said motor for moving said
distance setting member to focus said lens, means responsive to focussing
of said lens for stopping and holding said distance setting member at a
predetermined position, a home switch for detecting predetermined movement
of said distance setting member independently of the position of said
distance setting member after said reverse direction movement of said
distance-setting member, said home switch being operated with a delay
following movement of said distance setting member from said initial
position, means for coupling said home switch to said drive member, and
control means responsive to the operation of said home switch following
movement of said distance-setting member away from said initial position,
for detecting movement of said distance-setting member.
4. An automatic focusing system for a camera comprising a motor means
rotatable in first and second opposite directions, a drive member driven
for rotation in said directions by said motor means, a distance-setting
member rotatably driven by said drive member upon movement of said motor
means in said first direction to a predetermined position to place an
objective lens in an initial position, a holding mechanism for holding
said distance-setting member in said predetermined position, detecting
means coupled to said drive member and independent of the position of said
distance setting member for detecting the rotation of said drive member to
a given position as said motor is rotating in said second direction
following rotation of said distance-setting member in said first
direction, said detecting means being operable to generate a position
identification signal, and control means for controlling the sequence of
movements of said distance-setting member from a starting position to said
predetermined position, thereby preventing malfunction of the system and
reducing the focusing movement of said holding means.
5. An automatic focusing system for a camera according to claim 4, further
comprising means for selectively preventing holding of said
distance-setting member by said holding means at said initial position.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to automatic focusing systems for a
camera and in particular, to an automatic focusing system which can
analyze a sequence of movements of a distance-setting or focusing member
from an initial position to a focal position.
2. Description of the Related Art
A conventional automatic focusing system for a camera typically includes an
objective lens focusing mechanism mounted to a shutter unit as shown in
FIG. 6. A drive member 1 is rotatably mounted to a base plate 2 of the
shutter unit and has a sector gear 1a operatively connected through an
idler gear 3 to a stepper motor 4. The stepper motor 4 is rotatable in
both directions according to a predetermined program to drive the drive
member 1 for focusing, exposure and returning purposes. An operating cam
1b extends radially and outwardly from its outer periphery and cooperates
with an operating lever 5 to open and close a shutter (not shown).
A distance-setting member 6 has a drive portion 6a designed to move an
objective lens (not shown) to a focal position and is mounted to the base
plate 2 of the shutter unit, like the drive member 1. The distance-setting
member 6 also has a sector gear 6b in meshing engagement with a pinion 7a
which is, in turn, integrated with a ratchet wheel 7. A spring 6c is
arranged to rotate the distance-setting member 6 in a clockwise direction
together with the drive member 1. An engaging lever or pawl 8 is pivotally
mounted to the base plate 2 by a pin and biased by a spring 8a to rotate
in a clockwise direction. The pawl 8 has an iron piece 9a which is
attracted to an electromagnet 9. When the electromagnet 9 (also referred
to as an AF magnet) is rendered nonmagnetized, then the pawl 8 is rotated
in a clockwise direction to allow its free end to come into engagement
with teeth of the ratchet wheel 7. This holds the distance-setting member
6 in a focal position.
A pinion 11a is fixedly mounted to one end of the stepper motor 4 and is
operatively connected to the drive member 1. When the stepper motor 4 is
rotated in a reverse direction, the pinion 11a causes the ratchet wheel 7
to rotate in a clockwise direction via the drive member 1, a pin on the
cam 1b, and the distance-setting member 6. The pawl 8 is then moved out of
engagement with the teeth of the ratchet wheel 7, the free end of which is
held in a position away from the teeth of the ratchet wheel 7 upon
energization of the electromagnet 9.
In a focusing mode of operation, the stepper motor 4 is rotated in a
clockwise direction to drive the drive member 1 through the pinion 11a.
The distance-setting member 6 is then rotated in a clockwise direction
under the action of the spring 6c. A scanning lever (not shown) has a
luminous element which is operative to provide a light beam upon the
rotation of the distance-setting member 6. Such a light beam is reflected
from the subject and is then received by a light receiving element (not
shown). A focus signal is correspondingly developed so as to visually
display distance information within the field of view of a camera
viewfinder. Also, the electromagnet 9 is rendered nonmagnetized so as to
allow the pawl 8 to rotate in a clockwise direction. This causes the pawl
8 to come into meshing engagement with the ratchet wheel 7 and thus
restrains rotation of the distance-setting member 6. As a result, the
objective lens is held in its focal position.
Upon further rotation of the stepper motor 4, the drive member 1 is rotated
in a clockwise direction to cause the cam 1b to rotate the pin 5a of the
operating lever 5 in a counterclockwise direction. The stepper motor 4 no
longer controllably drives the distance-setting member 6 and is, in turn,
active to open and close a shutter for exposure purposes. It will be noted
that the stepper motor 4 can be rotated in a clockwise or counterclockwise
direction in response to phase pulses from a stepper motor drive circuit
4a.
The distance-setting member 6, when held in a starting position, is
constantly urged by the spring 6c to rotate in a clockwise direction. At
this time, a home switch Hs, as a means for identifying the position of
the distance-setting member 6, is held in an open state. This home switch
Hs is closed when the distance-setting member 6 is moved from a starting
position to a focal position. This indicates that the distance-setting
member 6 is properly moved in a sequential manner.
In such a conventional automatic focusing system, the home switch Hs is
mounted to the pin 6d of the distance-setting member 6. With this
arrangement, the stepper motor 4 is rotated in a reverse direction so as
to rotate the ratchet wheel 7 in a clockwise direction. The pawl 8 is then
moved out of engagement with the teeth of the ratchet wheel 7. The free
end of the pawl 8 is thus held in a position away from the teeth of the
ratchet wheel 7. The distance-setting member 6 is released at the time of
release of a first tooth of the ratchet wheel and then is free to rotate
in a reverse direction through the pinion 7a to thereby close the home
switch Hs. A minimum stroke is required for such rotation of the
distance-setting member 6. Normally, the teeth of the ratchet wheel 7
correspond to 30 to 40 steps. However, such a minimum stroke of the
ratchet wheel 7 requires eight pulses and occupies 20% of the teeth of the
ratchet wheel 7. Thus, this stroke can not be used for focusing purposes.
The teeth of the ratchet wheel 7 and the free end of the pawl 8 are
precisely finished in a manner to avoid improper engagement therebetween.
If the first tooth of the ratchet wheel 7 is not properly engaged with the
pawl 8, the distance-setting member 6 is not moved properly.
SUMMARY OF THE INVENTION
In view of the foregoing, it is an object of the present invention to
provide an automatic focusing system for a camera which includes means for
identifying the position of a drive member at each monitoring point and
means for analyzing the sequence of movement of a distance-setting member
in an exposure mode of operation, thereby reducing any possible
ineffective stroke of a ratchet wheel.
It is another object of the invention to provide an automatic focusing
system for a camera wherein means is provided to prevent improper
engagement of a distance-setting member with the first tooth of a ratchet
wheel so as to properly carry out an exposure mode of operation.
Briefly stated, in accordance with the invention, an automatic focusing
system for a camera has a reversible motor coupled to drive a drive
member, such as a drive ring. The drive member is coupled to drive a
distance-setting member, such as a range ring. The range ring is coupled
to control the positioning of an objective lens. The lens is movable from
an initial position, to a forward position to focus the lens on an object.
A distance detecting arrangement detects the distance to an object, and
controls a holding arrangement to hold the lens the forward position. The
position of the drive member is detected at a number of monitoring points
during a focusing operation, to produce position identification signals.
The position identification signals are analyzed in order to ensure that
the focusing operation has been properly effected.
BRIEF DESCRIPTION OF THE DRAWINGS
A better understanding of the invention made be had by reference to the
following detailed description of a preferred embodiment when taken in
conjunction with the accompanying drawings, in which:
FIG. 1 is a view showing an automatic focusing system for a camera
constructed according to one embodiment of the present invention;
FIG. 2 is a block diagram of a system for controlling the automatic
focusing system shown in FIG. 1;
FIGS. 3 and 4 are flow diagrams of programs for controlling the automatic
focusing system shown in FIG. 1;
FIG. 5 is a graph showing time vs. operating conditions of the drive
member, AF magnet, home switch and sector according to the program shown
in FIGS. 3 and 4; and
FIG. 6 is a view showing a conventional automatic focusing system for a
camera.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Reference will now be made to an automatic focusing system for a camera
constructed according to the invention, by way of example, shown in FIG. 1
through FIG. 4. Equivalent elements in FIG. 5 will be identified with the
same reference numerals.
Referring first to FIG. 1, a drive member 1 includes a projection extending
radially outwardly from its outer periphery and having a pin 1c thereon. A
home switch Hs is normally open and has a movable contact h.sub.1. A free
end of the movable contact h.sub.1 is supported by the pin 1c. When the
drive member 1 is rotated in a clockwise direction, the movable contact
h.sub.1 is brought into contact with a fixed contact h.sub.2.
A signal is developed in response to opening and closing of the home switch
Hs and then, fed to a main controller 19 in a central processing unit
through a data bus 20 as shown in FIG. 2.
At points FH.sub.1, FH.sub.2 and FH.sub.3 in a sequence analysis program
ANL shown in FIG. 3, sequence monitoring points SOB.sub.1, SOB.sub.2,
SOB.sub.3 are active to find whether the home switch Hs is on or off.
Also, at point SOB.sub.4 in a light measurement/exposure program EXC.sub.3
shown in FIG. 4, a monitoring point SOB.sub.4 is active to find whether
the home switch Hs is on or off. At point FH'.sub.1 in a process execution
program EXC.sub.2, the monitoring point SOB.sub.1 is active to find
whether the home switch Hs is off or not.
As shown in FIG. 2, a pulse generator 15, an AF magnet drive unit 16, a
shutter speed arithmetic unit 17, and a focus arithmetic unit 18 all
receive data from a light measurement unit 17a and a rangefinder 18a and
are controlled according to the programs EXC.sub.1 to EXC.sub.5 and ANL.
Operation of a release button SW shown in FIG. 2, whether it is on or off,
is monitored at point F.sub.1 in a distance determination program
EXC.sub.1 (FIG. 3). When the release button SW is on, a power hold is set
to H at point F.sub.2. At point F.sub.3, the distance of an object is
determined. Thereafter, the sequence analysis program ANL is initiated to
analyze the operating condition of the home switch Hs at monitoring points
SOB.sub.1, SOB.sub.2 and SOB.sub.3 to find whether the home switch Hs is
on or off. When it is found that the home switch Hs is not properly
operated, then a process indicator PI is set to 1, 2 or 3 to initiate the
process execution program EXC.sub.2. When it is found that the home switch
Hs is properly operated, then the process indicator PI is set to 8 to
initiate the light measurement/exposure program EXC.sub.3.
At point FH.sub.1 in the sequence analysis program ANL, the monitoring
point SOB.sub.1 is active to monitor the operating condition of the home
switch Hs. When the home switch Hs is properly operated, then three pulses
are generated to rotate the stepper motor 4 in a reverse direction at
point F.sub.4, the AF magnet is rendered magnetized at point F.sub.5, and
another three pulses are generated to rotate the stepper motor 4 in a
clockwise direction at point F6.
Next, at point FH.sub.2, the monitoring point SOB.sub.2 is active to
monitor the operating condition of the home switch Hs. When the home
switch Hs is properly operated, single pulses are sequentially generated
to rotate the stepper motor 4 in a clockwise direction at point F.sub.14
until the process of driving the objective lens is completed at point
F.sub.9. As noted earlier, the process indicator PI is then set to 8
(PI=8) at point F.sub.15. In the process of driving the objective lens,
when five pulses have been generated to rotate the stepper motor 4 in a
clockwise direction at point F.sub.10, the monitoring point SOB.sub.3 is
active to monitor the operating condition of the home switch Hs to find
whether or not it is on at point FH.sub.3. If the total number of pulses
generated are other than five, then the objective lens is stopped at point
F.sub.12, the AF magnet is rendered nonmagnetized at point F.sub.13, and
one pulse is generated to rotate the stepper motor 4 in a clockwise
direction at point F.sub.14.
The process execution program EXC.sub.2 will be executed as follows: When
PI=1, four pulses are first generated to rotate the stepper motor in a
reverse direction at point F.sub.17. At point F.sub.18, one is added to a
counter. At point F.sub.19, it is found how many times (n times) such
operation has been repeated. At point FH'.sub.1, the monitoring point
SOB.sub.1 is active to monitor the operating condition of the home switch
Hs to find whether it is off or not. If the home switch Hs is properly
operated, then the process indicator PI is set to zero (0) so as to
initiate the light measurement/exposure program EXC.sub.3. When PI=2, the
AF magnet is rendered nonmagnetized at point F.sub.21. Four pulses are
then generated to rotate the stepper motor 4 in a reverse direction at
point F.sub.22. When PI=3, the AF magnet is rendered nonmagnetized at
point F.sub.23. Nine pulses are then generated to rotate the stepper motor
in a reverse direction at point F.sub.24.
The light measurement/exposure program EXC.sub.3 shown in FIG. 4 will be
executed as follows. When the process indicator PI is neither zero (0) nor
eight (8), the system malfunctions (illegal function ILL), and an alarm is
provided according to a predetermined program (not shown). When PI=0, the
power hold is set to L at point F.sub.25 to terminate the whole operation.
When PI=8, the system is properly operated. At point F.sub.26, the AF
magnet is rendered nonmagnetized or off. At point F.sub.27, the intensity
of light is measured. At point F.sub.28, the AF magnet is rendered
magnetized or on. At point F.sub.29, an exposure mode of operation is
initiated. At point F.sub.30, the AF magnet is again rendered
nonmagnetized or off. At point F.sub.31, the distance-setting member 6 is
returned to its initial position.
At point FH.sub.4, the monitoring point SOB.sub.4 is active to monitor the
operating condition of the home switch Hs to find whether it is off or
not. When the home switch Hs is properly operated, the improper engagement
preventing program EXC.sub.4 is initiated. If not properly operated, then
a one is added to the counter at point F.sub.32. At point F.sub.33, the
number (P) of outputs is found. At point F.sub.34, four pulses are
generated to rotate the stepper motor 4 in a reverse direction. The
monitoring point SOB.sub.4 is again active to determine whether the home
switch Hs is properly operated.
The improper engagement preventing program EXC.sub.4 has a subroutine
F.sub.35 wherein two pulses are generated, one for clockwise rotation of
the stepper motor 4 and another for counterclockwise rotation thereof.
This program is intended to ensure proper engagement of the first tooth of
the ratchet wheel 7 with the pawl 8.
In a film advance program EXC.sub.5, a film is advanced by a single stroke
at point F.sub.36. At point F.sub.37, the process indicator P.sub.1 is set
to zero (0). Then, the power hold is set to L at point F.sub.25.
The operation is as follows. In the automatic focusing system of the
present invention thus constructed, after the distance determination
program EXC.sub.1 has been completed, at point FH.sub.1 in the sequence
analysis program ANL, the monitoring point SOB.sub.1 is active to find
whether the home switch Hs is off or not. If the home switch Hs is off,
then three pulses are generated for reverse rotation as shown at point
F.sub.4. The drive member 1 is thus rotated from an angle of .theta..sub.1
to an angle of .theta..sub.2. At point F.sub.5, the AF magnet is rendered
magnetized or is turned on. At point F.sub.6, three pulses are generated
for clockwise rotation. The drive member 1 is rotated to an angle
.theta..sub.1 ' to reach the monitoring point SOB.sub.2. When eight pulses
are generated, then the drive member 1 is rotated to an angle of
.theta..sub.3 to reach the monitoring point SOB.sub.3. Finally, at point
FH.sub.4 in the light measurement/exposure program shown in FIG. 4, the
monitoring point SOB.sub.4 is active to find whether the home switch Hs is
off or not. At point F.sub.31, the drive member is returned to its initial
position. The lens returning process occurs from point F.sub.31 to point
FH.sub.4.
When the drive member 1 is rotated to the maximum angle .theta..sub.4, the
sector (not shown) is opened by the operating cam of the drive member 1 in
an exposure process.
Illustratively, mechanical contacts are used to form the home switch.
Alternatively, semiconductor elements such as a photocoupler may be used.
Also, the drive member and the distance-setting member may be linearly
positioned. The motor may be an ultrasonic motor.
Advantages of the invention are as follows:
In accordance with the present invention, an automatic focusing system for
a camera comprises a motor rotatable in both directions, a drive member
driven for rotation by the motor, a distance-setting member rotatable
together with the drive member to place an objective lens in an initial
position and movable to a predetermined forward position, a holding
mechanism for holding said distance-setting member in said predetermined
forward position, means for identifying the position of said drive member
at each monitoring point, said means being operable to generate a position
identification signal, and means for analyzing a sequence of movement of
said distance-setting member from a starting position to said
predetermined forward position. This arrangement can identify the position
of the drive member at each sequence monitoring point, thereby preventing
malfunction of the system and reducing the focusing stroke of the holding
mechanism.
Also, in accordance with the present invention, an automatic focusing
system for a camera comprises a motor rotatable in both directions, a
drive member driven for rotation by the motor, a distance-setting member
rotatable together with the drive member to place an objective lens in an
initial position and movable to a predetermined forward position, a
holding mechanism for holding the distance-setting member in the
predetermined forward position, means for identifying the position of the
drive member at each monitoring point, the means being operable to
generate a position identification signal, means for analyzing the
sequence of movement of the distance-setting member from a starting
position to the predetermined forward position, and means for preventing
improper holding of the distance-setting member at the initial position.
An advantage with this arrangement is that improper holding of the
distance-setting member can be prevented.
Although the preferred embodiment of the present invention has been
described in detail, it will be understood that many variations and
changes may be made therein without departing from the spirit of the
invention or the scope of the appended claims.
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